Environmental and climate issues, as well as a concern about the sufficiency of fossil energy sources, have brought up a need for alternative energy sources. Renewable biomaterials represent a sustainable natural resource, but the utilization thereof as a substituent for fossil energy sources presents all in all one of the most extensive challenges for the future society from the standpoint of technology, economy, and ecology. The production of transportation fossil fuels alone is immensely large-scale business, and even a partial replacement of this production with biofuels calls for a significant technological leap in order to make the processing of biomaterials viable in large-scale industrial production. Indeed, a leading thought in this technological development is to work out the way of utilizing comprehensively and effectively the limited biomass and its various forms as components applicable to the manufacture of biofuel.
The natural processing of a biomaterial into biofuel could be ideally based on a microbiological process, wherein a biomass with a relatively low average energy content is used for producing components suitable for the manufacture of biofuel. A biotechnological mode of production that has been proposed in literature is the microbiological production of single-cell oil.
Based on generally known literature, the production of single-cell oil can be regarded as including steps of producing single-cell organisms, allowing the cells to produce oil, extracting and recovering the oil (Ratledge et al., 2005, Ratledge and Hopkins, 2006, Ratledge and Wilkinson, 1988 and 1989, Meng et al., 2009).
One of the proposed applications for single-cell oil has been its use as a special oil, in reference to health functionality or nutritional aspects. In this type of single-cell production processes, with moderate output rates, the biomaterials used as a feedstock, the individual operations, and costs incurred thereby, do not constitute an essential commercial obstacle in view of the expected value of the product.
Methods involving essentially the same process steps have also been described in reference to producing single-cell oil for use as components of biofuel. (Ratledge and Cohen 2008). In these processes, the recovered oil is processed for an alcohol ester of fatty acids, especially for methyl ester.
Hence, the basic technology for producing single-cell oil (subsequently “single-cell fat”) is known. However, the prior known technology does not provide adequate preconditions neither for commercially viable nor ecologically sustainable biofuel process (Ratledge and Cohen 2008). This is revealed even by a rough examination of carbon balance. As for the biomass feedstock used for a single-cell production process, about a third is released as carbon dioxide and about 40-80% of the remaining biomass consists of residual biomass after the extraction of oil. Based on a theoretical study alone, it can be noticed that, regarding the carbon contained in biomass used as a feedstock, the maximum recovery in the form of fat is about 30%. In practice, the carbon balance will be even remarkably lower than that, e.g. for the reason that the large amount of process water required by a microbiological process shall retain plenty of feedstock-based organic matter in a dilute and therefore hard-to-exploit form.
From the aspect of energy balance, as well, the prior art single-cell fat process is quite problematic. A still unanswered question is how the biomass, consisting of cell residues after the removal of oil, could be processed energy efficiently and how the organic carbon matter, present in the process water in a dissolved or dispersed dilute form, could be reclaimed and processed in energy efficient ways.
A solution for the poor overall use of biomass in the biotechnological manufacture of transportation fuel has been proposed in patent publication WO 2008134836. The solution described in the cited patent publication relates to the production of fat from a side fraction obtained in the treatment of sugar cane to make it suitable for the manufacture of ethanol. The discussed side fraction is used for cultivating autotrophic algae and fat-accumulating yeast.
With regard to this problem area, it has been proposed in patent publications WO 2009046375 and US 20090064567 A1 that spent nutrient solution residues and cell residues be treated in a way of making the same useful as a nutrient for microorganisms for providing polyunsaturated fatty acids or for implementing the production of methyl esters of ethanol or fatty acids. According to the cited publications, the discussed side streams call for diverse treatments, undermining the viability of using large side stream amounts.
The use of prior known single-cell fat production processes, according to the prior art, is not economically sensible, nor is it consistent with sustainable development to use such processes, especially for the large-scale manufacture of transportation fuel.